The present invention relates to pneumatic pressure control systems and, more particularly, to a system for controlling a pressure in an accumulator which is included in an air piping of a vehicle and shared by various loads such as air brake units or air suspension units.
All the known pressure control systems of the type described respond only to the accumulator pressure in controlling the same. An unloading valve mounted on a compressor is communicated with the accumulator by a pressure feedback circuit in which a governor is disposed. As the pressure inside the accumulator rises beyond a predetermined level, the governor is opened to condition the compressor into a relief or decompression state through the unloading valve. Upon drop of the accumulator pressure beyond a second predetermined level, the governor is closed to cause the compressor to compress input air. It is a common practice to preset a differential between the first and second predetermined pressure levels in order to prevent the governor from chattering.
However, the controlled operation of the compressor occurs without any relation with the running conditions of the engine, though being related with the pressure in the accumulator only. Accordingly, the compressor tends to be driven to an excessive extent while the engine runs at a heavy load, thereby affecting the operation of the vehicle.